This application is related to Japanese Patent Application No. 2001-172988 filed in Jun. 7, 2001, whose priority is claimed under 35 USC xc2xa7119, the disclosure of which is incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a magnetic information recording medium, and particularly to a vertical magnetic-recording magnetic information recording medium including a backing layer made of a soft magnetic film.
2. Description of the Related Art
Conventionally, a hard disk is used as a magnetic information recording medium. The hard disk is such that a magnetic layer made of CoCr alloy or the like is laminated on a disk-like nonmagnetic substrate of glass or the like.
A hard disk device is such that recording and reproduction of data is carried out by rotating the hard disk at high speed and causing a magnetic head for recording and reproduction to approach this hard disk.
A conventional hard disk uses an in-plane magnetic recording system in which anisotropy is provided in an in-plane direction of the disk, and at present, the disk having a capacity of about 20 Gbit/inch2 is realized by this system.
Besides, in recent years, in order to deal with a request for higher density, a vertical magnetic-recording is proposed in which track recording density (density in a track direction) of the disk is raised.
In the vertical magnetic-recording hard disk, information is recorded in a magnetic film (for example, TbFeCo) having perpendicular magnetic anisotropy. Besides, in the vertical magnetic-recording, there is proposed a hard disk in which in order to record and reproduce information in this magnetic film at high density and high efficiency, a soft magnetic film as a backing layer is provided between a substrate and a magnetic film (Japanese Unexamined Patent Publication No. Hei 6 (1994)-76202).
The backing layer is formed as a film having in-plane magnetic anisotropy, and this layer is such that a high magnetic field is obtained by magnetic interaction generated between a magnetic head and the backing layer to efficiently carry out vertical magnetic recording in the magnetic film. Here, from a viewpoint of recording and reproduction efficiency, a magnetic material having low coercive force is used for the backing layer.
For example, an FeNi alloy film (FeNi), a CoZr alloy film (CoZrNb), an inter-metallic compound film (FeTaC) or the like is used as the backing layer.
The formation of the backing layer on the substrate is carried out in such a manner that an alloy target of FeNi or the like or an inter-metallic compound target of FeTaC or the like is used, an external magnetic field of about 100 oersted (Oe) is applied, and sputtering onto the substrate is performed in a high temperature state of about 250xc2x0 C.
However, the conventionally used backing layer has problems that a medium noise is produced in a low frequency region, saturation magnetization is low, and formation of the in-plane magnetic anisotropy is difficult, and particularly in the point of high reliability of signal quality of recording and reproduction, it does not reach a practical level.
For example, in the case where FeNi alloy is used for the backing layer, since the saturation magnetization Ms is about 1500 emu/cc and is sufficiently high, there is no problem in the recording efficiency. However, in order to form the in-plane magnetic anisotropy necessary for recording and reproduction, as set forth before, it is necessary to form this backing layer by applying the external magnetic field and in the heating state of about 250xc2x0 C., and the adjustment of this temperature and the magnetic field is not easy. Besides, since a magnetic domain size is large, a large medium noise (about 80 xcexcVrms) in a low frequency region is produced.
In the case where CoZr alloy is used for the backing layer, in-plane magnetic anisotropy excellent for recording and reproduction can be formed. However, since the saturation magnetization Ms is as low as about 900 emu/cc, there is a problem in recording efficiency. Besides, a medium noise of about 10 xcexcVrms in a low frequency region is also produced, and practically sufficient reliability can not be obtained.
Further, in the case where FeTaC is used for the backing layer, in order to form in-plane magnetic anisotropy necessary for recording and reproduction, it is necessary to carry out the formation by applying an external magnetic field and in a heated state of about 350xc2x0 C. The saturation magnetization Ms is about 1100 emu/cc and is small as compared with FeNi alloy, and accordingly, there is a problem in recording efficiency. Besides, a medium noise of about 30 xcexcVrms in a low frequency region is also produced, and practically sufficient reliability can not be obtained.
Accordingly, in the backing layer made of the conventionally used material, it is difficult to suppress the medium noise in the low frequency region while a large saturation magnetization required in practical use is provided, and it is difficult to secure reliability of recording and reproduction to such a degree that a practical problem does not occur.
Further, in FeNi alloy or the like, in order to form in-plane magnetic anisotropy sufficient for recording and reproduction at the time of formation of the backing layer, it is necessary to carry out sputtering of the alloy material under the conditions of application of the external magnetic field and the high temperature.
The present invention is a magnetic information recording medium which is provided with a backing layer made of a soft magnetic film of a substantially amorphous structure and has a high saturation magnetization Ms and a low medium noise in a low frequency region.
Besides, the object of the invention is to form a backing layer having a practical in-plane magnetic anisotropy without applying an external magnetic field and under a room temperature environment.
This invention provides a magnetic information recording medium comprising a backing layer containing Fe and C as its main ingredient, having a substantially amorphous structure, and having an easy axis of magnetization in an in-plane direction, and a magnetic layer having an easy axis of magnetization in a vertical direction and recording information.